In the widely used keg tapping systems of the type to which the present invention generally relates, each keg is fitted with a keg unit that is seated in its bung hole and comprises normally closed valves thaat are opened by installation on the keg of a coupler or tapping unit. The keg installation defines an upwardly opening well in which the coupler or tapping unit is receivable, and the bottom of the well is defined by an annular gas valve seat, a concentric annular gas valve which is biased upwardly for engagement with the gas valve seat and which itself defines a liquid valve seat, and a central poppet-like liquid valve that is biased upwardly for engagement with the liquid valve seat. When the keg is tapped, beer flows up to the liquid valve through a siphon tube which extends down to near the bottom of the keg, being forced up the siphon tube by pressure gas filled into the keg past the open gas valve.
A coupler or tapping unit to be coupled to the keg conventionally has a substantially annular outer body member that is received in the well and makes a bayonet connection with lugs on the keg that project radially into the well near its top. When that bayonet connection is established, a radially inner body member of the coupler is moved down to open the gas and liquid valves in the keg and thus communicate the interior of the keg with gas and liquid passages in the coupler.
In a tavern installation, the liquid passage in the coupler is more or less permanently connected with a duct that leads to a beer tap at the bar, while the gas passage in the coupler is connected with a source of pressure gas (usually a bottle of compressed carbon dioxide) from which the interior of the keg is pressurized.
When keg beer is purchased for consumption at a party or picnic, it is delivered in a keg having a valve installation identical to the one in a keg delivered to a tavern, but it is obviously impractical to provide a bottle of pressure gas, along with the plumbing and pressure control valves that are normally incorporated in the pressure gas system of a tavern installation. For such occasions, therefore, the keg is tapped by means of a portable tapping unit in which there is incorporated a hand pump that can be used for pressurizing the keg.
Most prior portable tapping couplers were basically tavern units that had been modified by the addition of a hand pump, but the above identified copending application discloses a portable tapping unit that is substantially less expensive and substantially more compact than a modified tavern unit and has other desirable features, including an easily operated hand pump.
The present invention is especially suitable for the portable tapping unit of said copending application, but it also lends itself to portable couplers of other types. The problem that it solves is one that has heretofore been common to all types of portable tapping units.
When a keg of beer is to be tapped, the interior of the keg is almost invariably under some gas pressure. Such pressure develops during filling of the keg and is increased by any subsequent rise in the temperature of the keg contents. When the keg is coupled to a tavern system, this so-called racking-off pressure is of no consequence because the duct that leads from the keg to the tap is refrigerated and the beer thus arrives at the tap outlet at a temperature and under a pressure no higher than it had in the keg. With a portable coupler, however, the beer flows out through an unrefrigerated duct, and if the pressure in the keg is too high, the gas in the beer will come out of solution as it flows to the tap. The result is the heretofore common and annoying experience that the first few glasses of beer drawn from a keg tapped at a party or picnic are "wild"--that is, almost entirely foam. After the outlet duct cools with flow of beer through it and keg pressure is reduced by withdrawal of beer, the beer appears to settle and is dispensed with no more than a desirable head of foam. Thereafter it is necessary to give the hand pump a few strokes from time to time, to maintain enough pressure in the keg for steady dispensing of beer. An excessive use of the hand pump at any time will again result in several glasses of wild beer being drawn. However, the hand pump in the coupling unit of said copending application is so arranged as to offer noticeably high resistance to operation when the keg is adequately pressurized, thus discouraging such pressurization as would cause wild beer to be dispensed.